What did the ozone layer develop?

The ozone layer developed as a result of the accumulation of ozone (O₃) in the Earth's stratosphere, primarily due to the interaction of ultraviolet (UV) radiation from the sun with oxygen molecules (O₂). This process, known as the ozone-oxygen cycle, began around 2.4 billion years ago, coinciding with the Great Oxidation Event when atmospheric oxygen levels rose significantly. The formation of the ozone layer is crucial as it absorbs the majority of the sun's harmful UV radiation, protecting living organisms and enabling life to thrive on Earth.